Thymus serpyllum extracts express antioxidative, antispasmodic, anti-inflammatory, antihypertensive, cytotoxic, antiseptic, antibacterial, and antifungal activities due to the presence of polyphenols. Polyphenol compounds from T. serpyllum extracts are sensitive to temperature, light, oxidation, and pH changes, possess low bioavailability, and have a bitter taste. Thus, despite their great bioactive potential, their application in different industries is quite limited. Liposomes can enhance the stability of encapsulated sensitive compounds and the bioavailability of poorly hydrosoluble components. Additionally, liposomal particles have outstanding biodegradability and a strong affinity for cells. Furthermore, the bilayer membrane of liposomes and its permeability can be modified by adding sterols, such as ergosterol, which can change the end product’s properties and pharmacological behavior. Thus, the antioxidant activity of ergosterol–phospholipid liposomes with encapsulated T. serpyllum ethanol extract was examined. The DPPH and ABTS radical scavenging activity and ferric ion-reducing potential of the extract-loaded liposomes with different proportions of ergosterol (10 and 20 mol %) were investigated. The percentage neutralization of DPPH radicals for the samples with 10 and 20 mol % of ergosterol was 56.3±2.2% and 53.1±3.5%, respectively. The elimination of ABTS radicals was significantly higher and amounted to 95.3±2.6% (10 mol % of ergosterol) and 98.2±1.7% (20 mol % of ergosterol). The Fe³⁺-reducing potential of the liposomes was 0.14±0.01 mmol FeSO4/L and 0.15±0.03 mmol FeSO₄/L (for 10 and 20 mol % of ergosterol, respectively). Therefore, there was no significant difference between the antioxidant capacity of the liposomes with differing amounts of ergosterol. Using LC/DAD/MS analysis, the polyphenol compounds identified in the encapsulated extract included chlorogenic, caffeic, rosmarinic, and salvianolic acids, salvianolic acid K isomer, 6,8-Di-C-glucosylapigenin, 6-hydroxyluteolin 7-O-glucoside, luteolin 7-O-glucuronide, and apigenin glucuronide. The antioxidant potential demonstrated in this study highlights the potential applications of liposomes prepared with ergosterol and active compounds of T. serpyllum extract in functional foods, pharmaceutics, or cosmetics.